In order to expedite the installation of electrical conduits in modern buildings, relatively short lengths of such conduits (for example 10 feet) are first arranged and bound into prefabricated assemblies of one or more layers of spaced-apart conduits. These prefabricated conduit assemblies are subsequently transported to and installed on the underside of the roof or ceiling in a building under construction. During such installation, the conduit assemblies are serially aligned end-to-end and the abutting ends of the conduits of two different assemblies are coupled together to form a multiplicity of parallel, room-traversing electrical conduits.
The method most often used throughout the electrical industry for prefabricating the conduits into multiple-conduit assemblies and mounting them in a building is generally referred to as the “trapeze” system. In this system, a pair of rail-like struts having a row of uniformly-spaced clamps is used to secure the opposite ends of a row of perhaps five or six 10 foot conduits. Each of the rail-like struts has a “U” shaped cross-section into which a plurality of pairs of clamping straps may be slidably positioned. The bottom ends of each pair of clamping straps include recesses that slidably receive the rail-like edges of the struts, while the top ends include a bolt hole through which a clamping bolt is inserted. After sliding the ends of a series of conduits between the clamping straps, the clamping bolts of each of the pairs of clamping straps are tightened. Such bolt tightening pulls the top ends of the straps against the sides of the conduit while forcing the bottom ends of the straps outwardly into frictional engagement with the rail-like edges of the struts. The resulting conduit assemblies may be serially installed on the underside of the building roof or ceiling with the ends of the conduits in adjacent assemblies in alignment. Conduit couplings are then used to interconnect the abutting ends of the conduits of two adjacent conduit assemblies.
Conduit spacing and mounting systems which use spacer plates are also known in the prior art. The spacer plates in such systems have one or more rows of conduit-receiving, circular holes for receiving a conduit and maintaining it in a desired lateral position with respect to adjacent conduits. The conduits are secured against longitudinal movement relative to the plate openings by either a bendable tab that radially extends into the conduit-receiving holes and frictionally engages the conduit, or by a set screw mounted in a cantilevered flange provided along an edge of the spacer plate adjacent to the row of conduit-receiving holes.